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Why is there no empty char literal?

Is there any specific reason why there is no empty char literal?
What comes closest to what I think of, the '' is the '\0' the null character.
In C++ the char is represented by an int, which means empty char goes directly to the 0 integer value, which is in C++ "the same as null".
The practical part of coming up with that question:
In a class I want to represent char values as enum attributes.
Unbiased I tried to initialize an instance with '', which of course does not work.
But shouldn't be there a char null value? Not to be confused with string.Empty,
more in the nature of a null reference.
So the question is: Why is there no empty char?
-edit-
Seeing this question the question can be enhanced on:
An empty char value would enable concatening strings and chars without
destroying the string. Would that not be preferable? Or should this
"just work as expected"?

A char by definition has a length of one character. Empty simply doesn't fit the bill.
Don't run into confusion between a char and a string of max length 1. They sure look similar, but are very different beasts.

To give a slightly more technical explanation: There is no character that can serve as the identity element when performing concatenation. This is different from integers, where 0 serves as the identity element for addition.

String must be exactly one character long

I have what I think is an easy problem. For some reason the following code generates the exception, "String must be exactly one character long".
int n = 0;
foreach (char letter in charMsg)
{
// Get the integral value of the character.
int value = Convert.ToInt32(letter);
// Convert the decimal value to a hexadecimal value in string form.
string hexOutput = String.Format("{0:X}", value);
//Console.WriteLine("Hexadecimal value of {0} is {1}", letter, hexOutput);
charMsg[n] = Convert.ToChar(hexOutput);
n++;
}
The exception occurs at the charMsg[n] = Convert.ToChar(hexOutput); line. Why does it happen? When I check the values of CharMsg it seems to contain all of them properly, yet still throws an error at me.
UPDATE: I've solved this problem, it was my mistake. Sorry for bothering you.
OK, this was a really stupid mistake on my part. Point is, with my problem I'm not even supposed to do this as hex values clearly won't help me in any way.
What I am trying to do it to encrypt a message in an image. I've already encrypted the length of said message in last digits on each color channel of first pixel. Now I'm trying to put the very message in there. I lookt here: http://en.wikipedia.org/wiki/ASCII and said to myself without thinking that usung hexes would be a good idea. Can't belive I thought that.

Convert.ToChar( string s ), per the documentation requires a single character string, otherwise it throws a FormatException as you've noted. It is a rough, though more restrictive, equivalent of
public char string2char( string s )
{
return s[0] ;
}
Your code does the following:
Iterates over all the characters in some enumrable collection of characters.
For each such character, it...
Converts the char to an int. Hint: a char is an integral type: its an unsigned 16-bit integral value.
converts that value to a string containing a hex representation of the character in question. For most characters, that string will be at least two character in length: for instance, converting the space character (' ', 0x20) this way will give you the string "20".
You then try to convert that back to a char and replace the current item being iterated over. This is where your exception is thrown. One thing you should note here is that altering a collection being enumerated is likely to cause the enumerator to throw an exception.
What exactly are you trying to accomplish here. For instance, given a charMsg that consist of 3 characters, 'a', 'b' and 'c', what should happen. A clear problem statement helps us to help you.

Since printable unicode characters can be anywhere in range from 0x0000 to 0xFFFF, your hexOutput variable can hold more than one character - this is why error is thrown.
Convert.ToChar(string) would always check length a of string, and if it is not equal to 1 - it would throw. So it would not convert string 0x30 to hexadecimal number, and then to ascii representation, symbol 0.
Can you elaborate on what you are trying to archieve ?

Your hexOutput is a string, and I'm assuming charMsg is a character array. Suppose the first element in charMsg is 'p', or hex value 70. The documentation for Convert.ToChar(string) says it'll use just the first character of the string ('7'), but it's wrong. It'll throw this error. You can test this with a static example, like charMsg[n] = Convert.ToChar("70");. You'll get the same error.
Are you trying to replace characters with hex values? If so, you might try using a StringBuilder object instead of your array assignments.

Convert.ToChar(string) if it is empty string lead this error. instead use cchar()

Casting non-numeric char to int?

I came across this line of code today:
int c = (int)'c';
I was not aware you could cast a char to an int. So I tested it out, and found that a=97, b=98, c=99, d=100 etc etc...
Why is 'a' 97? What do those numbers relate to?

Everyone else (so far) has referred to ASCII. That's a very limited view - it works for 'a', but doesn't work for anything with an accent etc - which can very easily be represented by char.
A char is just an unsigned 16-bit integer, which is a UTF-16 code unit. Usually that's equivalent to a Unicode character, but not always - sometimes multiple code units are required for a single full character. See the documentation for System.Char for more details.
The implicit conversion from char to int (you don't need the cast in your code) just converts that 16-bit unsigned integer to a 32-bit signed integer in the natural, non-lossy way - just as if you had a ushort.
Note that every valid character in ASCII has the same value in UTF-16, which is why the two are often confused when the examples are only ones from the ASCII set.

97 is UTF-16 code unit value of letter a.
Basically this number relates to UTF-16 code unit of given character.

These are the ASCII values representing the characters.

They are the decimal representation of their ascii counterpart:
http://www.asciitable.com/index/asciifull.gif
so 'a' would be a 97

They are character codes, commonly known as ASCII values.
Technically, though, the character codes are not ASCII.

What does this C# string format mean?

From my previous question, Converting chinese character to Unicode, I had a good answer but with some code I didn't understand:
Console.WriteLine("U+{0:x4}", (int)myChar);
Could anyone explain this?

Console.WriteLine("U+{0:x4}", (int)myChar);
is the equivalent to the call:
Console.WriteLine("U+{0}", ((int)myChar).ToString("x4"));
In a format string, the : indicates that the item should be displayed using the provided format. The x4 part indicates that the integer should be printed in its hexadecimal form using 4 characters. Refer to standard numeric format strings for more information.

The 0 indicates which positional argument to substitute. The x displays a hexadecimal number, the 4 has it display four digits.
For example, the character ȿ (LATIN SMALL LETTER S WITH SWASH TAIL, codepoint 575) is printed as U+023F since 57510 = 23F16.

That will simply create the literal string "U+1234"... now if you are wanting to convert a unicode code point into a char, you want Convert.ToChar(myChar)
http://msdn.microsoft.com/en-us/library/3hkfdkcx.aspx

C# Build hexadecimal notation string

How do I build an escape sequence string in hexadecimal notation.
Example:
string s = "\x1A"; // this will create the hex-value 1A or dec-value 26
I want to be able to build strings with hex-values between 00 to FF like this (in this example 1B)
string s = "\x" + "1B"; // Unrecognized escape sequence
Maybe there's another way of making hexadecimal strings...

Please try to avoid the \x escape sequence. It's difficult to read because where it stops depends on the data. For instance, how much difference is there at a glance between these two strings?
"\x9Good compiler"
"\x9Bad compiler"
In the former, the "\x9" is tab - the escape sequence stops there because 'G' is not a valid hex character. In the second string, "\x9Bad" is all an escape sequence, leaving you with some random Unicode character and " compiler".
I suggest you use the \u escape sequence instead:
"\u0009Good compiler"
"\u0009Bad compiler"
(Of course for tab you'd use \t but I hope you see what I mean...)
This is somewhat aside from the original question of course, but that's been answered already :)

You don't store hexadecimal values in strings.
You can, but it would just be that, a string, and would have to be cast to an integer or a byte to actually read its value.
You can assign a hexadecimal value as a literal to an int or a byte though:
Byte value = 0x0FF;
int value = 0x1B;
So, its easily possible to pass an hexadecimal literal into your string:
string foo = String.Format("{0} hex test", 0x0BB);
Which would create this string "126 hex test".
But I don't think that's what you wanted?

There's an '\u' escape code for hexadecimal 16 bits unicode character codes.
Console.WriteLine( "Look, I'm so happy : \u263A" );